Evaluation of reticulocyte counts by flow cytometry in a routine laboratory

Reticulocyte counting using flow cytometry and a membrane-permeable fluorescent dye, thiazole orange, was evaluated as an alternative to the conventional manual method. The flow cytometric method was more precise (mean c.v. of 4.3%) than the imprecise manual technique (mean c.v. of 22.4%). Linearity was highly acceptable (r = 0.99) over the reticulocyte count range of 1.8-30.1%. Flow cytometry allows processing of large numbers of samples with reduction in technologist time, and the improved precision and tenfold increase in the number of cells counted should considerably improve the clinical utility of the reticulocyte count.